/*
  * Copyright (c) 2012 Stefano Sabatini
  *
  * This file is part of FFmpeg.
  *
  * FFmpeg is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
  * License as published by the Free Software Foundation; either
  * version 2.1 of the License, or (at your option) any later version.
  *
  * FFmpeg is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Lesser General Public License for more details.
  *
  * You should have received a copy of the GNU Lesser General Public
  * License along with FFmpeg; if not, write to the Free Software
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
 /**
  * @file framestep filter, inspired on libmpcodecs/vf_framestep.c by
  * Daniele Fornighieri <guru AT digitalfantasy it>.
  */
 
 #include "avfilter.h"
 #include "internal.h"
 #include "video.h"
 
 typedef struct {
     int frame_step, frame_count, frame_selected;
 } FrameStepContext;
 
 static av_cold int init(AVFilterContext *ctx, const char *args)
 {
     FrameStepContext *framestep = ctx->priv;
     char *tailptr;

     long int n = 1;

 
     if (args) {
         n = strtol(args, &tailptr, 10);
         if (*tailptr || n <= 0 || n >= INT_MAX) {
             av_log(ctx, AV_LOG_ERROR,
                    "Invalid argument '%s', must be a positive integer <= INT_MAX\n", args);
             return AVERROR(EINVAL);
         }
     }
 
     framestep->frame_step = n;
     return 0;
 }
 
 static int config_output_props(AVFilterLink *outlink)
 {
     AVFilterContext *ctx = outlink->src;
     FrameStepContext *framestep = ctx->priv;
     AVFilterLink *inlink = ctx->inputs[0];
 
     outlink->frame_rate =
         av_div_q(inlink->frame_rate, (AVRational){framestep->frame_step, 1});
 
     av_log(ctx, AV_LOG_VERBOSE, "step:%d frame_rate:%d/%d(%f) -> frame_rate:%d/%d(%f)\n",
            framestep->frame_step,
            inlink->frame_rate.num, inlink->frame_rate.den, av_q2d(inlink->frame_rate),
            outlink->frame_rate.num, outlink->frame_rate.den, av_q2d(outlink->frame_rate));
     return 0;
 }
 

 static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *ref)

 {
     FrameStepContext *framestep = inlink->dst->priv;
 
     if (!(framestep->frame_count++ % framestep->frame_step)) {
         framestep->frame_selected = 1;

         return ff_filter_frame(inlink->dst->outputs[0], ref);
     } else {
         framestep->frame_selected = 0;
         avfilter_unref_buffer(ref);
         return 0;

     }
 }
 
 static int request_frame(AVFilterLink *outlink)
 {
     FrameStepContext *framestep = outlink->src->priv;
     AVFilterLink *inlink = outlink->src->inputs[0];
     int ret;
 
     framestep->frame_selected = 0;
     do {
         ret = ff_request_frame(inlink);
     } while (!framestep->frame_selected && ret >= 0);
 
     return ret;
 }
 

 static const AVFilterPad framestep_inputs[] = {
     {
         .name             = "default",
         .type             = AVMEDIA_TYPE_VIDEO,
         .get_video_buffer = ff_null_get_video_buffer,

         .filter_frame     = filter_frame,

     },
     { NULL }
 };
 
 static const AVFilterPad framestep_outputs[] = {
     {
         .name          = "default",
         .type          = AVMEDIA_TYPE_VIDEO,
         .config_props  = config_output_props,
         .request_frame = request_frame,
     },
     { NULL }
 };
 

 AVFilter avfilter_vf_framestep = {
     .name      = "framestep",
     .description = NULL_IF_CONFIG_SMALL("Select one frame every N frames."),
     .init      = init,
     .priv_size = sizeof(FrameStepContext),

     .inputs    = framestep_inputs,
     .outputs   = framestep_outputs,

 };